A century of Toxoplasma gondii research

Toxoplasma gondii (Fig. 1) is a protozoan parasite that can be transmitted directly from cats to humans through faecal contamination of food, or indirectly from cats to livestock and then to humans through undercooked meat. Around 30% of humans in the United Kingdom are infected, and as such, harbour dormant cysts in their brain, but few have overt symptoms of disease. Neurological disease can occur in these people if they become immunosuppressed (Fig. 2). The possibility that apparently healthy people with infection are more likely to develop psychiatric disease, including schizophrenia and depression, is under investigation. Infection during pregnancy can cause abortion or foetal infection. Congenital disease can result in systemic, neurological and progressive eye disease

Structural and functional studies of histidine biosynthesis in Acanthamoeba spp. demonstrates a novel molecular arrangement and target for antimicrobials

Acanthamoeba is normally free-living, but sometimes facultative and occasionally opportunistic parasites. Current therapies are, by necessity, arduous and yet poorly effective due to their inabilities to kill cyst stages or in some cases to actually induce encystation. Acanthamoeba can therefore survive as cysts and cause disease recurrence. Herein, in pursuit of better therapies and to understand the biochemistry of this understudied organism, we characterize its histidine biosynthesis pathway and explore the potential of targeting this with antimicrobials. We demonstrate that Acanthamoeba is a histidine autotroph, but with the ability to scavenge preformed histidine. It is able to grow in defined media lacking this amino acid, but is inhibited by 3-amino-1,2,4-triazole (3AT) that targets Imidazoleglycerol-Phosphate Dehydratase (IGPD) the rate limiting step of histidine biosynthesis. The structure of Acanthamoeba IGPD has also been determined in complex with 2-hydroxy-3-(1,2,4-triazol-1-yl) propylphosphonate [(R)-C348], a recently described novel inhibitor of Arabidopsis thaliana IGPD. This compound inhibited the growth of four Acanthamoeba species, having a 50% inhibitory concentration (IC50) ranging from 250-526 nM. This effect could be ablated by the addition of 1 mM exogenous free histidine, but importantly not by physiological concentrations found in mammalian tissues. The ability of 3AT and (R)-C348 to restrict the growth of four strains of Acanthamoeba spp. including a recently isolated clinical strain, while not inducing encystment, demonstrates the potential therapeutic utility of targeting the histidine biosynthesis pathway in Acanthamoeba

Pregnancy and susceptibility to parasites

This chapter discusses pregnancy and susceptibility to parasites

A rare case of mixed infectious keratitis caused by Pseudomonas koreensis and Aspergillus fumigatus

We report the clinical and microbiological features of contact lens-related mixed infectious keratitis caused by a spore-forming filamentous fungus and a rare gram-negative bacterial infection. A 66-year-old Caucasian female presented with right eye (OD) pain after sleeping in her 2-weekly contact lenses for 3 days. On presentation, corrected distance visual acuity was 0.46 LogMAR OD and 0.20 in the left eye. Slit lamp biomicroscopy revealed a 1.9 mm by 1.9 mm area of dense stromal infiltrate with epithelial defect. Corneal scrapes grew <i>Aspergillus fumigatus</i> and <i>Pseudomonas koreensis</i>, and culture-directed microbial therapy with oral and topical voriconazole and topical fortified gentamicin along with regular debridement resulted in slow resolution of the infection, leaving a dense stromal scar in the visual axis requiring penetrating keratoplasty. Mixed infectious keratitis caused by filamentous fungi and gram-negative bacteria is rare. <i>Pseudomonas koreensis</i> infection has not been previously reported as a cause of infectious keratitis in humans. In our experience, these mixed infections require prolonged systemic and topical therapy and the secondary scarring may require surgical intervention for vision rehabilitation

Anemia in salmon aquaculture:Scotland as a case study

Anemia in salmonid aquaculture is a recognized blood disorder resulting from the reduction of hemoglobin concentration and/or erythrocyte count. Because of sub-optimal oxygen supply to the tissues, as a negative impact of anemia fish will experience reduced growth and poor health. This health challenge may be linked with several factors including anthropogenic changes in the marine environment, infectious etiology (viral, bacterial, and parasitic), nutritional deficiencies, or hemorrhaging. From the mid-late summer of 2017 to 2019, Scottish salmon farming companies began to report the occurrence of anemic events in open-net marine sites. At that time, the industry had little understanding of the pathogenesis and possible mechanisms of anemia and limited the ability to formulate effective mitigation strategies. Clinical examination of fish raised suspicion of anemia and this was confirmed by generating a packed cell volume value by centrifugation of a microhematocrit tube of whole anticoagulated blood. Company health team members, including vets and biologists, reported discoloration of gills and local hemorrhages. This paper reviews various commercially significant cases and lesser-known cases of anemia in cultured salmonid species induced by various biological factors. The current methods available to assess hematology are addressed and some future methods that could be adopted in modern day fish farming are identified. An account of the most recent anemic event in Scottish farmed Atlantic salmon (Salmo salar) is presented and discussed as a case study from information provided by two major Scottish salmon producers. The percent of total marine sites (n = 80) included in this case study, that reported with suspected or clinical anemia covering the period mid-late summer 2017 to 2019, was between 1 and 13%. The findings from this case study suggest that anemia experienced in most cases was regenerative and most likely linked to blood loss from the gills

DNA vaccination against the parasite enzyme gamma-glutamylcysteine synthetase confers protection against Leishmania donovani infection

In this study the potential of using Leishmania donovani gamma-glutamylcysteine synthetase (glutamate-cysteine ligase, gamma-GCS) as a rational target for vaccine development was determined. Mice, immunised with plasmid containing the full gene sequence for gamma-GCS (pVAX-gamma GCS) or plasmid alone (pVAX control), were challenged with a high dose of L. donovani amastigotes to give a stringent test of the ability of the vaccine to protect against infection. Vaccination with pVAX-gamma GCS resulted in the production of specific IgG1 and IgG2a antibodies and resulted in significantly lower liver parasite burdens compared to controls. Protection was also associated with a significant increase in cell-mediated immunity, demonstrated as an increase in nitrite production by ConA stimulated splenocytes, an increase in the percentage of splenic CD3(+)CD4(+) cells, and enhanced granuloma maturation, compared to control values. (C) 2007 Elsevier Ltd. All rights reserved

Comparative assessment of a DNA and protein Leishmania donovani gamma glutamyl cysteine synthetase vaccine to cross-protect against murine cutaneous leishmaniasis caused by L. major or L. mexicana infection

Leishmaniasis is a major health problem and it is estimated that 12 million people are currently infected. A vaccine which could cross-protect people against different Leishmania spp. would facilitate control of this disease as more than one species of Leishmania may be present. In this study the ability of a DNA vaccine, using the full gene sequence for L. donovani gamma glutamyl cysteine synthetase (?GCS) incorporated in the pVAX vector (pVAX?GCS), and a protein vaccine, using the corresponding recombinant L. donovani ?GCS protein (Ld?GCS), to protect against L. major or L. mexicana infection was evaluated. DNA vaccination gave transient protection against L. major and no protection against L. mexicana despite significantly enhancing specific antibody titres in vaccinated infected mice compared to infected controls. Vaccination with the Ld?GCS protected against both species but only if the protein was incorporated into non-ionic surfactant vesicles for L. mexicana. The results of this study indicate that a L. donovani ?GCS vaccine could be used to vaccinate against more than one Leishmania species but only if the recombinant protein is used